What principle suggests that every contact leaves a trace?

The principle that suggests "every contact leaves a trace" is known as Locard's Exchange Principle. This foundational concept in forensic science asserts that whenever two objects come into contact with one another, there is always a transfer of material from one to the other. This means that perpetrators of crimes will inevitably leave behind traces of their presence at a crime scene, whether in the form of hair, fibers, fingerprints, or other physical evidence.

Understanding this principle is crucial for investigators as it guides forensic analysis and evidence collection. Locard’s Exchange Principle emphasizes the importance of meticulously searching for and preserving contact traces that can tie a suspect to a crime scene, thereby contributing significantly to the investigation. This principle underlines that all interactions result in some form of evidence exchange, which can be pivotal in establishing connections between individuals, places, and actions.